Re: Tech Tip - Winchester Model 100
Many rifles will jam if closed on a fired case, especially one that was not fired in that rifle. The case swelled when fired, and then jams when forced into the chamber. It doesn't happen with unfired cases or when firing. It is just bad luck that the boresighter was the right (or wrong) size and jammed in the chamber. A little light oil on it might have helped prevent the problem.
When loading for any semi-auto, you should full length resize and use the special sizing dies that are a bit smaller than the standard.